1. Field of the Invention
The present invention relates to a power supply control system for a vehicle.
2. Description of Related Art
Recently, many electrical apparatuses and electronic devices are installed in a vehicle, and their electric power demand is tending on the rise. Under such circumstances, a conventional method, whereby electricity is generated through operating a generator only by mechanical power of an engine, has caused concern about deterioration in gas mileage and acceleration performance by consuming most of the engine mechanical power on generating electricity, and about a decrease in a supply voltage and exhaustion of a battery due to a supply power shortage.
Accordingly, an art (e.g., JP10-309002A) is proposed to seek to solve the above problem by recovering energy other than the engine mechanical power, particularly the energy that is conventionally wasted, and generating electricity (i.e., by regenerating the energy). For example, according to JP10-309002A, a regenerative deceleration device generates electricity from kinetic energy at a decelerating time of the vehicle.
Besides the regenerative deceleration device in JP10-309002A, an exhaust heat generator, which generates electricity from heat energy of a coolant of the engine, is proposed. The exhaust thermoelectric generator employs a Rankine cycle of condensation and expansion of a refrigerant. More specifically, the refrigerant is expanded by the heat energy of the engine coolant, and then the kinetic energy generated from the expansion of the refrigerant is converted into rotational energy by an expander, thereby driving the generator to generate electricity. On the assumption that the exhaust thermoelectric generator is connected to a power supply system of the vehicle to supply electric power (exhaust thermoelectrically generated power) generated from exhaust heat, if the exhaust thermoelectrically generated power is smaller than the electric power required for an electric load of the vehicle (an electric power load of the vehicle), a difference between the electric power load and the exhaust thermoelectrically generated power can be generated by an alternator through voltage control by a regulator of the alternator of the vehicle. Consequently, the electric power generated by the alternator (mechanically generated electric power that is generated from the engine mechanical power by the alternator) becomes smaller by as much electric power as is generated from the exhaust heat, thereby reducing a load applied to the alternator and thus saving an engine fuel.
Nevertheless, in supplying the exhaust thermoelectrically generated power to the power supply system of the vehicle, in which the regenerative deceleration device in JP10-309002A is installed, if the electric power, which is supplied both by the regenerative deceleration device and by the electric power from the exhaust heat, exceeds an upper voltage limit of the power supply system, the power supply system cannot receive both the electric power at once, thereby reducing an effect of regenerative deceleration (or exhaust thermoelectric generation).
In such a case, the power supply system is allowed to increase the electric power that can receive both the electric power at once by raising an upper limit of a regulated voltage in controlling the voltage by the regulator. On the other hand, the battery is slightly overcharged, thereby shortening a life of the battery. Furthermore, although high-performance batteries such as a lithium battery and a nickel metal hydride (NiMH) battery may be employed in place of batteries that are poor in receiving a charge, such as a lead battery, adopting such high-performance batteries creates high production costs.
Moreover, if the exhaust thermoelectrically generated power is larger than the electric power required for the electric load of the vehicle, the alternator does not need to generate electricity at all, whereas the electric power generated by means of the regenerative deceleration is not received either. On the other hand, since the exhaust thermoelectric generation removes heat from the engine coolant, an excessive reduction in a coolant temperature due to undue electric generation may not only reduce the amount of the electric generation, but also have an adverse effect on the gas mileage and an emission.